The present invention relates to an optical pick-up head apparatus which can be used for recording and reproducing or erasing optical information on and from an optical storage medium such as an optical disc and an optical card.
The optical memory technique utilizing a high-density and large-capacity storage medium such as an optical disc to record information by a pit-like pattern has been practiced as digital audio disc, video disc, document file disc and data file and has become widely applied to many fields. The reliability of the recording/reproduction of the optical information greatly depends upon the performance of an optical pick-up head apparatus used. Recently, for mass production of an optical pick-up head apparatus, attempts to form optical devices on a semiconductor substrate are made, for example, the Japanese Utility Model Provisional Publication No. 58-162660 discloses a semiconductor apparatus in which a semiconductor laser, a reflector and a photodetector are formed in the same semiconductor substrate and the Japanese Patent Provisional Publication No. 2-52487 discloses an optical pick-up head apparatus in which a surface emitting laser is disposed on a photodetector. Further, the Japanese Patent Provisional Publications Nos. 1-46243, 1-150244 and 2-253678 disclose optical pick-up head apparatus in which a photodetector and a reflector are formed in one semiconductor substrate and a semiconductor laser is disposed on the same semiconductor substrate.
FIG. 1 shows a conventional semiconductor apparatus as exemplified in the Japanese Utility Model Provisional Publication No. 58-162660. In FIG. 1, in this apparatus, on a semiconductor substrate 1 there are formed a semiconductor laser element 2 and a reflection surface 3 whereby a laser beam emitted from the semiconductor laser 2 is reflected in a direction perpendicular to a surface of the semiconductor substrate 1 as indicated by an arrow A. Further, a photodetector 4 is disposed on the surface of the semiconductor substrate 1 to receive an incident light beam as indicated by an arrow B. FIG. 2 shows an optical pick-up head apparatus using as a light source the semiconductor apparatus as shown in FIG. 1, which apparatus is exemplified in the Japanese Patent Provisional Publication No. 64-27286. In FIG. 2, the laser beam A emitted from the semiconductor laser 2 and then reflected on the reflection surface 3 passes through a holographic optical element 5 and is converged by an objective lens 6 to be focused on an optical storage medium 7. At this time, the laser beam A is intensity-modulated in accordance with information recorded in the optical storage medium 7 and reflected therefrom. This reflected beam again passes through the objective lens 6 to be incident on the holographic optical element 5. Here, this holographic optical element 5 has a function to generate a diffraction beam having an astigmatic aberration with respect to the reflected beam from the optical storage medium 7. This diffraction beam from the holographic optical element 5 is incident as the beam B on the photodetector 4. The photodetector 4 is divided into four areas which outputs electric signals in correspondence with the incident beams, respectively. The electric signals of the four-divided photodetector 4 are supplied to an adequate electric circuit to perform appropriate operations to provide a focusing error (FE) signal, a tracking error (TE) signal and an information (RF) signal corresponding to the information signal recorded on the optical storage medium 7.
In FIG. 2 optical pick-up head apparatus, since the semiconductor laser 2 and the photodetector 4 are formed on the same semiconductor substrate 1, the alignment therebetween can be made with an extremely high accuracy below 1 micron. However, the holographic optical element 5 is constructed as a different part spatially separated therefrom, and hence, in assembling the optical pick-up head apparatus, there is a problem that the holographic optical element 5 is required to be rotationally adjusted so that the beam from the holographic optical element 5 is incident on a desired position on the photodetector 4.